Elapsed time indicators, such as hourglasses, have been known since ancient times. More modern elapsed time indicators have extremely diverse and varied constructions. For example electronic timers can be utilized, manual indicators can be advanced by a user, a soluble glass disk can dissolve in water, or brush bristles can irreversibly change color. However the majority of such prior art elapsed time indicators have several significant disadvantages or limitations associated therewith. For example some of them, such as hourglasses, are limited to relatively short periods of time, others, such as electronic timers, are complex and relatively expensive, others, such as those which irreversibly change color, cannot be effectively reused, while still others are not suitable for use in association with products that will be ingested by humans.
According to the present invention an elapsed time indicator, and various specific embodiments for use thereof, is provided which is inexpensive, essentially infinitely reusable, can be used to determine a wide variety of different time periods (including time periods of more than a month), may be used in contact with human ingestible materials, yet still is accurate. Particularly desirable applications of the elapsed time indicator are to time the usage of water treatment filters, and to time the storage period for perishable foods, however the variety of uses of the elapsed time indicator according to the present invention is virtually infinite.
According to one aspect of the present invention an elapsed time indicator is provided comprising the following elements: A substantially transparent and substantially straight tube having first and second ends, an interior, and an exterior. A viscous liquid substantially filling the interior of the tube. A visible indicator immersed in the viscous liquid and dimensioned and positioned with respect to the tube so that the visible indicator can travel from the first end to the second end through the viscous liquid and vice versa. And, the liquid and the visible indicator being selected so that there is a known predetermined time period for the visible indicator to travel through the liquid between the first and second ends when the tube has a particular orientation with respect to the vertical.
Preferably the visible indicator is substantially spherical, and the interior diameter of the tube is about twice the diameter of the visible indicator. In this case, the predetermined time period can be precisely (for all practical purposes) calculated. The predetermined time period is determined by L/S where L is the distance between the first and second ends of the tube location of the visible indicator in cm, and S.sup.= (2/9)R.sup.2 A.DELTA.D/V, where S=the speed of the spherical visible indicator in cm/s, R=the radius of the spherical visible indicator in cm, .DELTA.D=the density difference between the spherical visible indicator and the fluid in gm./cm.sup.3, A=the acceleration of gravity (981 cm./s.sup.2), and V=the absolute viscosity of the fluid in gm./cm second.
The time indicator can include means for releasably holding the visible indicator in a stationary position at one of the ends thereof until activated. For example the tube may be of a flexible plastic material, at least adjacent the first end thereof, and the releasable holding means may comprise a clamp for deforming the tube to clamp the visible indicator to the tube until the clamp is released. Alternatively the visible indicator can be of magnetic material (e.g. of magnetic ferris hydroxide--magnetite--in wax), and the releasable holding means may comprise a magnet.
The viscous liquid (the term "liquid" being used very generically to include gels or other semi-solids, or semi-liquids) can be of a wide variety of materials, and preferably is a material that is not toxic to humans. For example one material that can be utilized is polydimethylsiloxane, such as available from General Electric by the trade name "Viscasil". Such a liquid typically has a kinematic viscosity of about 100,000 centistokes, but the viscosity of the liquid utilized according to the invention can vary widely depending upon the time period desired to measure from about 1,000 centistokes to well over 100,000 centistokes. The viscous liquid also must be compatible with the material of the tube, which may be glass, acrylic, or a flexible tubing material such as plastic tubing sold under the trademark "Tygon" by Norton Company of Worcester, Mass.
The visible indicator may take a wide variety of forms and constructions. Most commonly it would comprise a sphere of non-toxic solid material, such as high density polypropylene, or wax. If a magnetic indicator is desired a blend of magnetite in wax can be provided. However the visible indicator need not be a solid at all but can be a fluid immiscible in the viscous liquid. For example annato oil, or dyed water are both immiscible in silicone oil and form round beads. However when using fluid visible indicators it may be necessary to treat the interior of the tube so that the indicating fluid does not wet the inside of the tube and stick to it when the end of travel position is reached. The visible indicator can be of any color, which preferably clearly contrasts with the color of the viscous liquid, for example black, red, high visibility orange, white, etc.
It is also possible to utilize more than one visible indicator within a tube, or to provide a plurality of tubes in line or adjacent each other so that a differential and speed of movement of the indicators can be provided. Also there is no necessity that either the tube or the indicator have a circular cross-section, but rather they may be distinctly non-circular, such as polygonal in cross-section in the case of the tube, and polygonal, cross-shaped, or the like, in the case of the visible indicators.
Typically the tube is mounted during use so that it is generally vertical (precisely vertical, or at some angle to the vertical that is known, but not horizontal). The mounting means can mount the tube so that it can be inverted so that either end may be disposed vertically above the other, or so that it can be readily removed from the mount and inverted and then replaced in the mount.
The visible indicator and viscous liquid can be selected (by changing the materials, shapes, and a wide variety of other variables) so that almost any desired passage of time can be indicated. The indicators according to the invention are perhaps most useful, however, when the indicate the passage of about one day or more for travel of the visible indicator from the first end of the tube to the second end, or vice versa, if the indicator is maintained at generally ambient temperatures (e.g. about 5.degree.-30.degree. C.). For some uses, such as for water filters, the passage of at least about 30 days (e.g. about 30-60 days) is a most desirable indicator time, while for a product shelf life the time period may be even greater than 60 days. The tube may also be mounted adjacent a scale or another graduated indicator so that the position of the visible indicator with respect to the tube can be easily discerned.
The indicator according to the invention is particularly desirable for use in or on a water bottle having a filter, which filter should be replaced or regenerated after the passage of the predetermined period of time. For example the elapsed time indicator according to the invention may be built directly in a tubular cap for the water bottle.
According to another aspect of the present invention a cap for a water bottle is provided comprising: A tubular cap body having interior and exterior side surfaces, and a top surface. Surface manifestations provided on the interior or exterior side surfaces for holding the cap body onto a bottle neck. The cap top surface including a transparent portion. An elapsed time indicator. And, means for mounting the elapsed time indicator radially interiorly of the cap body side surfaces so that the indicator is visible through the transparent portion of the cap body top surface.
The elapsed time indicator utilized in the cap as described above may comprise: A substantially transparent tube having first and second ends, and an interior; a viscous liquid substantially filling the interior of the tube; a visible indicator immersed in the viscous liquid; and the liquid and indicator being selected so that it takes the passage of at least about 30 days at a temperature range of about 5.degree.-30.degree. C. for the indicator to move from one end of the tube to the other; and wherein the means for mounting the elapsed time indicator mounts the tube so that one of the ends thereof is adjacent to and visible through the cap transparent portion, and so that the tube is generally vertical when the cap top surface is generally horizontal. The mounting means preferably firmly but releasably holds the tube in place, so that the tube may be removed from the cap and inverted and then replaced. Of course the tube, viscous liquid, and visible indicator are all made of materials non-toxic to humans in this embodiment.
It is the primary object of the present invention to provide an inexpensive, reusable (not requiring use or intervention except to view, and at the end of the elapsed time invert), and accurate elapsed time indicator, and structures for utilization thereof. This and other objects of the invention will become clear from an inspection of the derailed description of the invention, and from the appended claims.